Method for purification of substances contaminated with organic chemicals

ABSTRACT

The present invention provides a method for purifying organic chemical-containing contaminated substances by which various organic chemicals (contaminants) can be readily and sufficiently decomposed in a short time, the method comprising the steps of adding a metal salt and a transition metal ionic compound to water or soil that contains organic chemicals, decomposing the organic chemicals by irradiating with light, and separating/collecting the detoxified organic chemicals.

TECHNICAL FIELD

The present invention relates to a method for purifying an organicchemical-containing contaminated substance conducted in the presence ofat least one water-soluble alkali metal compound and/or at least onealkaline-earth metal compound, and at least one transition metal ioniccompound. The present invention also relates to a system for purifyingan organic chemical-containing contaminated substance.

BACKGROUND OF THE INVENTION

In recent years, environmental pollution caused by organic chemicals hasbecome a concern in many parts of the world. In particular, manyaromatic compounds possess biotoxicity, carcinogenicity, mutagenicity,endocrine disrupting activity, etc., and therefore their influence onhuman beings and ecosystems causes concern.

In order to prevent environmental pollution caused by organic chemicals,various laws and regulations have been enforced, but no satisfactoryeffect has yet been achieved. One of the probable causes of suchpollution is the discharge of industrial and domestic drainage, leachatefrom landfills, etc., without having been satisfactorily purified. Toprevent such environmental pollution, it is necessary to satisfactorilypurify polluted drainage, etc., before discharging it into thesurroundings.

Examples of organic chemicals that may cause environmental pollutioninclude alkylphenols, bisphenol A, dioxin, PCBs, etc. They are difficultto decompose, exhibit endocrine disrupting activity, and adverselyaffect human beings and ecosystems even at low concentrations.

Examples of methods for decomposing and/or removing such organicchemicals (also referred to herein as contaminants) include biologicalmethods utilizing microorganisms (for example, Non-patent Document 1),physical methods utilizing activated carbon and like adsorbents (forexample, Non-patent Document 2), chemical methods wherein organicchemicals are decomposed by being irradiated with ultraviolet light (forexample, Non-patent Document 3), etc. However, using biological methods,it is difficult to decompose a variety of contaminants with a singlemicroorganism, and therefore a microorganism suitable for eachcontaminant has to be found. Moreover, even if suitable microorganismsare obtained, it is necessary to create the conditions in which themicroorganisms can exhibit sufficient decomposition ability in actualpractice. Furthermore, since a microorganism can decompose a contaminantonly slowly, there is a problem in that the decomposition and removal ofthe contaminant takes time. In contrast, using physical methods,although various contaminants can be adsorbed, a separate step fortreating the collected contaminants becomes necessary. Using chemicalmethods, organic chemicals are decomposed only at a slow rate when usinga mild method and some organic chemicals cannot be decomposed at alldepending on the type thereof, and therefore the use of toxic chemicals(oxidants, strong acids, etc.) is necessary to accelerate thedecomposition of such organic chemicals.

In view of such circumstances, a method for decomposing and/or removingcontaminants in which various contaminants can be safely and readilytreated in a short time is being sought.

-   [Non-patent Document 1] World Journal of Microbiology &    Biotechnology, 20, 517-522 (2004)-   [Non-patent Document 2] Chemosphere, 58, 1535-1545 (2005)-   [Non-patent Document 3] Journal of Hazardous Materials, B101,    301-314 (2003).

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

One of main objects of the present invention is to provide a simplemethod for purifying organic chemical-containing contaminated substancesby which various organic chemicals (contaminants) can be readily andsufficiently decomposed in a short time, and a system for purifyingorganic chemical-containing contaminated substances.

Means for Solving the Problem

The present inventors found that, by adding a specific metal compoundand a transition metal ionic compound to organic chemicals(contaminants) and subjecting the resultant mixture to lightirradiation, contaminants can be effectively decomposed, and the organicchemicals become insoluble to form solid matter (insoluble matter fromthe decomposed organic chemicals) that can be easily removed. Methodsfor decomposing contaminants by irradiating light (ultraviolet lightirradiation) are known; however, the facts that the decomposition speedof various contaminants remarkably improves and contaminants that cannotbe decomposed by conventional techniques can be decomposed by addingspecific a metal compound(s), and insolubilization of the decomposedorganic chemicals can be promoted by adding a transition metal ioniccompound(s) such as cobalt chloride, etc., are newly found by thepresent inventors. The present invention has been accomplished based onthe above findings and by conducting further intensive research.

The present invention provides methods for purifying organicchemical-containing contaminated substances and a system for purifyingorganic chemical-containing contaminated substances as below.

Item 1. A method for purifying an organic chemical-containingcontaminated substance comprising a step of irradiating the organicchemical-containing contaminated substance with light in the presence of(i) at least one water-soluble alkali metal compound and/or at least onealkaline-earth metal compound, and (ii) at least one transition metalionic compound.Item 2. The method according to Item 1, which comprises a first step ofadding (i) at least one water-soluble alkali metal compound and/or atleast one alkaline-earth metal compound, and (ii) at least onetransition metal ionic compound to an organic chemical-containingcontaminated substance; and a second step of irradiating a mixtureobtained in the first step with light.Item 3. The method according to Item 1, wherein said at least onewater-soluble alkali metal compound and/or said at least onealkaline-earth metal compound is at least one member selected from thegroup consisting of calcium, magnesium, potassium, and sodium.Item 4. The method according to Item 1, wherein at least one of thecompounds (i) and (ii) is adhered to a carrier.Item 5. The method according to Item 1, wherein a compound comprisingthe compound (ii) adhered to the compound (i) is used as compounds (i)and (ii).Item 6. The method according to Item 1, wherein the compound (ii) is atleast one compound of a transition metal selected from the groupconsisting of cobalt, manganese, iron, nickel, copper, and zinc.Item 7. The method according to Item 1, which further comprises a thirdstep of separating insoluble matter generated from the organic chemicalafter irradiating the organic chemical-containing contaminated substancewith light.Item 8. The method according to Item 1, wherein the compound (i) isdolomite.Item 9. The method according to Item 1, wherein the organic chemical isan endocrine disruptor or an agricultural chemical.Item 10. The method according to Item 1, wherein the organic chemical isan organochlorine compound or an aromatic compound.Item 11. The method according to Item 1, wherein the organic chemical isa polychlorinated biphenyl (PCB) or dioxin.Item 12. The method according to Item 1, wherein the organic chemical isat least one member selected from the group consisting ofo-chlorophenol, p-chlorophenol, 2,4-dichlorophenol, p-tert-butylphenol,1-naphthol, 3,5-xylenol, carbendazim, 17β-estradiol and bisphenol A.Item 13. The method according to Item 1, wherein Compound (i) is addedto a contaminated substance in such a manner that the concentration ofCompound (i) is 0.00005-50 wt % calculated as a metallic salt unit.Item 14. The method according to Item 1, wherein Compound (ii) is addedto a contaminated substance in such a manner that the concentration ofCompound (ii) is 0.01 to 10 mM.Item 15. The method according to Item 1, wherein the light used forlight irradiation is ultraviolet.Item 16. The method according to Item 1, wherein the organicchemical-containing contaminated substance is at least one memberselected from the group consisting of factory effluents, agriculturaleffluents, domestic drainage, sewage, leachate from waste disposalsites, exhaust gases, contaminated soil, sludge and incinerated ash.Item 17. A method for purifying an, organic chemical-containingcontaminated substance comprising the steps of:

(I) irradiating the organic chemical-containing contaminated substancewith light in the presence of (i) at least one water-soluble alkalimetal compound and/or at least one alkaline-earth metal compound; andthen

(II) adding (ii) at least one transition metal compound.

Item 18. The method according to Item 17, which further comprises athird step of separating and collecting insoluble matter generated fromthe organic chemical after conducting steps (I) and (II).Item 19. A system for purifying an organic chemical-containingcontaminated substance comprising:

a photoreaction reactor for irradiating an organic chemical-containingcontaminated substance with light in the presence of at least onewater-soluble alkali metal compound and/or at least one alkaline-earthmetal compound, and at least one transition metal ionic compound.

Item 20. The system according to Item 19, which further comprisesseparation and collection equipment for separating and collectinginsoluble matter generated in the photoreaction reactor.

Effect of the Invention

Because a wide variety of contaminants can be treated under the sameconditions, the method for purifying organic chemical-containingcontaminated substances of the present invention is very useful forpurifying water, soil, etc., containing various kinds of organicchemicals. In the method for purifying organic chemicals of the presentinvention, because the decomposition speed is very fast, organicchemicals can be treated in a short time, and therefore this method canbe suitably employed to reduce the size of a purification system, totreat large amounts of waste water, etc. Furthermore, because decomposedorganic chemicals can be separated and collected as insoluble matter inthe method of the present invention, it can be concluded that the methodof the present invention is excellent in removing organic chemicals,which are contamination sources of contaminated substances, and usableas a method for purifying contaminated substances.

The method of the present invention is different from known methods inthat it does not mineralize organic chemicals, but polymerizes andinsolubilizes the decomposed organic chemicals to make them easilycollected, and achieves an excellent collection rate.

Furthermore, if the concentration of the organic chemicals contained incontaminated substance is low, it is difficult or impossible to purifythe contaminated substance by known methods. However, the method of theinvention can sufficiently purify even such a contaminated substance,and therefore it can be suitably used for purifying various contaminatedsubstances.

Dolomite can be used in the method of the present invention as a mixtureof (i) water-soluble alkali metal compounds and/or alkaline-earth metalcompounds. Dolomite hitherto has been used as foodstuffs, fertilizers,etc., and its safety is confirmed. Furthermore, because dolomite can beeasily obtained at low cost, the present invention can provide aninexpensive purification system.

As described above, the method for purifying organic chemical-containingcontaminated substances of the present invention is very simple, safe,highly practicable, and excellent in purifying water, soil and likecontaminated substances.

BEST MODE FOR CARRYING OUT THE INVENTION 1. Method for Purifying OrganicChemical-Containing Contaminated Substances

The present invention encompasses the following methods. A first methodis characterized in irradiating an organic chemical-containingcontaminated substance with light in the presence of (i) at least onewater-soluble alkali metal compound and/or at least one alkaline-earthmetal compound, and (ii) at least one transition metal ionic compound.

A second method is characterized in irradiating the organicchemical-containing contaminated substance with light in the presence of(i) at least one water-soluble alkali metal compound and/or at least onealkaline-earth metal compound; and then adding (ii) at least onetransition metal compound.

The first and second methods are explained in detail below.

[First Method]

In the First method of the present invention, light irradiation isconducted under the presence of (i) at least one water-soluble alkalimetal compound and/or at least one alkaline-earth metal compound, and(ii) at least one transition metal ionic compound.

The method for purifying organic chemical-containing contaminatedsubstances of the present invention primarily comprises the followingtwo steps:

(1) a first step of adding (i) at least one water-soluble alkali metalcompound and/or at least one alkaline-earth metal compound (this mayreferred to as Compound (i)), and (ii) at least one transition metalionic compound (this may referred to as Compound (ii)) to an organicchemical-containing contaminated substance, and mixing them ifnecessary; and

(2) a second step of irradiating the mixture obtained in the first stepwith light.

A third step (3), wherein insolubilized organic chemicals are separatedand collected, may follow the above-mentioned two steps, if necessary.

The method for purifying organic chemicals of the present invention isdescribed in detail below.

(1) First Step

In the first step, Compound (i) and Compound (ii) are added to acontaminated substance, which is contaminated with at least one organicchemical. In this step, it is preferable to mix Compound (i) andCompound (ii) with the organic chemical-containing contaminatedsubstance during or before irradiation of light.

(i) Water-Soluble Alkali Metal Compound and/or at Least OneAlkaline-Earth Metal Compound

Compound (i) usable in the present invention comprises an alkali metalor an alkali-earth metal and is water soluble. Specifically, Compound(i) includes hydroxides, inorganic-acid salts, organic acid salts,oxides, etc., of calcium, magnesium, potassium, and sodium.

Specific examples of Compound (i) include calcium hydroxide, magnesiumhydroxide, potassium hydroxide, sodium hydroxide and like hydroxides;calcium nitrate, calcium carbonate, magnesium nitrate, magnesiumcarbonate, potassium nitrate, potassium carbonate, sodium nitrate,sodium carbonate and like inorganic-acid salts; calcium acetate,magnesium acetate, potassium acetate, sodium acetate, calcium citrate,magnesium citrate, potassium citrate, sodium citrate and likeorganic-acid salts; and calcium oxide, magnesium oxide, potassium oxide,sodium oxide and like oxides.

Among these metal compounds, calcium hydroxide, calcium oxide, calciumcarbonat, magnesium hydroxide, magnesium oxide, magnesium carbonate,potassium hydroxide, and sodium hydroxide are preferable from aviewpoint of effective organic chemical decomposition.

The above-mentioned metal compounds may be used singly or incombination. Natural minerals may be used as Compound (i), and dolomiteis an example of such a natural mineral.

Dolomite may also be called as magnesian limestone that is a mixturecomprising calcium and magnesium as principal components. Dolomitecontains calcium carbonate, magnesium carbonate, calcium oxide,magnesium oxide, calcium hydroxide, magnesium hydroxide, etc. Theproportions of these constitutional components in the present inventionare not limited, and any natural dolomite can be used withoutmodification. Natural dolomite generally contains about 30 wt % calcium,and about 15 wt % magnesium, and the amount of dolomite used is suitablyselected based on the contents of these metals.

It is also possible to use processed dolomite obtained by calcining,hydrating and/or aging natural dolomite. Examples of such processeddolomite include soft-burned dolomite, digested dolomite, dolomiteclinker, dolomite plaster, magnesium calcium carbonate, etc.

The content of Compound (i) used in the present invention may besuitably adjusted so that the effects of the present invention may beattained, but it is preferable that Compound (i) be added in such amanner that the content of the metal compound(s) during the purificationprocess, i.e., when Compound (i) and Compound (ii) are added to acontaminated substance, is generally about 0.00005-50 wt %, andpreferably about 0.001-30 wt % calculated as a metallic compound unit.If the content of Compound (i) falls within an above range, all ofCompound (i) does not have to be dissolved in water and a portionthereof may exist in a form of solid matter or particles that areinsoluble in water. In the case of dolomite, it is preferable that thedolomite be mixed with organic chemicals in such a manner that thecontent of dolomite while irradiating with light is generally about0.0005-10 wt %, and preferably about 0.01-1 wt %. If the content ofCompound (i) or dolomite falls within an above range, wide variety oforganic chemicals can be efficiently decomposed.

(ii) Transition Metal Ionic Compound

In the present invention, “transition metal ionic compounds” means metalcompounds in which a transition metal becomes ions in an aqueoussolution or an aqueous solution of Compound (i).

Various known transition metal ionic compounds can be used in thepresent invention including manganese, iron, cobalt, nickel, copper,zinc, etc. Among these, cobalt and iron are preferable. Examples ofcompounds of these metals include cobalt chloride, cobalt bromide,cobalt sulfate, cobalt nitrate, cobalt hydroxide, cobalt carbonate,cobalt phosphorate, cobalt acetate, cobalt ethylenediaminetetraacetate,ferric chloride, iron sulfate, iron nitrate, iron hydroxide, ironphosphorate, iron ethylenediaminetetraacetate, etc. Among thesecompounds, cobalt chloride, cobalt sulfate, cobalt nitrate, ferricchloride, iron sulfate, and iron nitrate are preferable.

The content of the transition metal ionic compound used in the presentinvention may be suitably adjusted so that the effects of the presentinvention can be attained, but it is preferable that the transitionmetal ionic compound be added in such a manner that the content oftransition metal ionic compound during the purification process, i.e.,when Compound (i) and Compound (ii) are added to a contaminatedsubstance, is generally about 0.01-10 mM, and preferably about 0.1-1 mM.If the content of transition metal ionic compound falls within an aboverange, a variety of organic chemicals can be efficiently decomposed.

In the present invention, either or both of Compound (i) and Compound(ii) may be adhered to a carrier such as ceramics, activated carbon,etc.

Instead of using Compound (i) with Compound (ii), it is also possible touse a compound wherein Compound (ii) is adhered to Compound (i).

Organic Chemical-Containing Contaminated Substance

The organic chemicals to be decomposed by the method of the presentinvention are organic chemicals that cause environmental pollution.Examples of such organic chemicals include endocrine disruptors,agricultural chemicals, etc. Specific examples of endocrine disruptorsinclude polychlorinated dibenzo-p-dioxin (PCDD), polychlorinateddibenzofuran (PCDF) and like dioxins; coplanar polychlorinated biphenyland like polychlorinated biphenyls (PCBs); organochlorine compounds suchas o-chlorophenol, p-chlorophenol, 2,4-dichlorophenol and likechlorophenols; p-tert-butylphenol, 3,5-xylenol and like alkylphenols;bisphenol A, 1-naphthol and like aromatic compounds; 17β-estradiol andlike natural female hormones, etc. Examples of agricultural chemicalsinclude 2,4-dichlorophenoxyacetic acid (2,4-D), carbendazim, etc.

In particular, o-chlorophenol, 2,4-dichlorophenol, p-tert-butylphenol,1-naphthol, 3,5-xylenol, bisphenol A, 17β-estradiol, carbendazim, etc.,have extremely low decomposition rate when only conventional ultravioletlight irradiation is employed. However, by conducting light irradiationafter adding Compound (i), the decomposition efficiency is significantlyimproved and the decomposition rate is therefore increased. Furthermore,in the method of the present invention, by adding a transition metalionic compound as well as Compound (i), insolubilization of thedecomposed organic chemicals is facilitated, and insoluble matter havinga size easily filtered out is generated. In the present invention,insoluble matter means solid matter that is insoluble in water formedfrom insolubilized organic chemicals by being irradiated with light, andincludes flotage, precipitates, etc.

There is no limitation to the form of the above-mentioned organicchemicals, and they may be contained in, for example, soils; sludge,incinerated ashes; waters such as industrial and domestic drainage,sewage, rivers, leachate from landfills (water that has seeped from soilin waste disposal sites), etc.; agricultural products and likefoodstuffs; exhaust gases; waste generated in a space station, etc.

The organic chemical is mixed with Compound (i) (and a transition metalionic compound), and, preferably, agitated to make a homogeneousmixture. Water may be added to the mixture, if necessary. The amount ofwater added is not limited and can be suitably selected depending on theamount and state of the contaminated substance that contains organicchemicals, and the amounts of Compound (i) (and the transition metalionic compound).

The method of the present invention can sufficiently purify thecontaminated substance in wide concentration range of the organicchemicals between about 0.1 nM and about 1 M.

It is difficult or impossible to purify a contaminated substance byknown methods if the concentration of the organic chemicals containedtherein is unduly low. However, the method of the present invention isalso effective even if the concentration of the organic chemicals isvery low.

(2) Second Step

In the second step, the mixture obtained in the first step is irradiatedwith light.

Light Irradiation

A mixture such as an aqueous solution, slurry, etc., obtained in the (1)first step is irradiated with light. The light used is not limited aslong as it can irradiate the mixture. There is no limitation to theirradiation area, etc., but total irradiation is more advantageous asthis makes the decomposition reaction progress more efficiently. Inorder to uniformly irradiate the mixture with light, the mixture may beagitated while irradiating with light, or the light irradiation may beconducted in a reactor, etc. The light irradiation may be conducted atroom temperature or ambient temperature for about 0.1 second to about 24hours, preferably about 1 second to about 10 hours, more preferablyabout 10 seconds to about 3 hours.

Ultraviolet light is the most appropriate for use in light irradiation.There is no limitation to such types of light source as long as theyemit ultraviolet light. Examples of the light sources include sunlightand like natural lights; and fluorescent light, germicidal lamp, mercurylamp, deuterium lamp, xenon lamp, halogen lamp, tungsten lamp, LED andlike artificial lights.

The intensity of irradiation light varies depending on the type of thelight. There is no particular limit to the intensity of irradiationlight; however it is generally about 0.1 mWcm⁻² or more. The moreintense the light would be the better. For example, when ultravioletlight is used, generally about 0.1 mWcm⁻² or more, preferably about 0.1to about 1000000 mWcm⁻², more preferably about 1 to about 1000000mWcm⁻².

(3) Third Step

The insoluble matter generated in the second step may be separated andcollected in a third step.

Separation/Collection

In the present invention, by adding an ionic transition metal, organicchemicals can be insolubilized to form insoluble matter from thedetoxified organic chemicals, and therefore it is also possible toseparate and collect the thus-formed insoluble matter.

Known apparatuses and methods can be used for separating/collecting suchinsoluble matter, and a dust collector, column, filtration apparatus,cyclone, centrifugal separator, etc., can be suitably selected dependingon the status of the contaminated substance.

[Second Method]

Furthermore, the present invention also provides a purification methodcomprising the following steps:

(i) irradiating the organic chemical-containing contaminated substancewith light in the presence of at least one water-soluble alkali metalcompound and/or at least one alkaline-earth metal compound (this stepmay be referred to as Step (I)); and

(ii) adding at least one transition metal ionic compound afterconducting Step (I) (this step may be referred to as Step (II)).

The types of Compound (i) used in Step (I), types of contaminatedsubstance, types of organic chemical, conditions for light irradiation,etc., are the same as those in the above-explained First method. Theamount of Compound (i) are the same as the amount of Compound (i) addedto contaminated substance as described in First method above.

The amounts and types of Compound (ii) used in Step (II) are the same asthose in the above-explained First method.

In Step (II) of the second method, Compound (ii) is added to Compound(i) and an organic chemical-containing contaminated substance afterirradiation. These components are mixed if necessary, and then treatedat room temperature or ambient temperature for about 0.1 second to about24 hours, preferably about 1 second to about 10 hours, more preferablyabout 10 seconds to about 3 hours. The mixture may be agitated or heatedto accelerate the reaction, if necessary during the treatment therebythe organic chemicals is insolubilized.

Likewise the First method described above, a third step ofseparating/collecting the insolubilized organic chemicals may be addedin the Second method after conducting step II.

Application

The first and second purification methods of the present invention canbe applied to various contaminated substances such as water, incineratedash, soil, sludge, foodstuffs, organic solvents, oils, exhaust gases,etc.

For example, in the case of purifying contaminated water, thecontaminated water is stored in a reactor, reservoir, etc., and Compound(i) (and a transition metal ionic compound) is added thereto, followedby light irradiation so that the organic chemicals contained can bedecomposed. In the method of the present invention, insolubilization ofthe organic chemicals is facilitated by adding at least one transitionmetal ionic compound, forming detoxified insoluble matter. By filtering(separating) this insoluble matter, organic chemicals can be removedfrom waste water. Neutralization of the treated waste water can bereadily conducted by known methods (for example, adding acid, etc.).

Alternatively, it is possible to decompose the organic chemicalscontained in the contaminated water by passing the contaminated waterthrough a column filed with Compound (i) (and a transition metal ioniccompound) to obtain an aqueous solution containing Compound (i) (and thetransition metal ionic compound), and then conducting light irradiation.

One example of a method for purifying contaminated soil and/orincinerated ash is that Compound (i) (and a transition metal ioniccompound), and water if necessary, are added to the soil, etc., to forma slurry, and the thus-formed slurry is irradiated with light whilebeing agitated in a reactor. In this case, the decomposed organicchemicals are detoxified and insolubilized, forming solid matter(insoluble matter). Therefore, insoluble matter of the decomposedorganic chemicals remains in the post-treated soil but separation isunnecessary.

In the case of purifying exhaust gases, a solution containing Compound(i) and a transition metal ionic compound can be sprayed into the spacecontaining exhaust gas in the presence of water vapor, and lightirradiation is then conducted. It is also possible to purify exhaustgases by spraying small particles containing Compound (i) and atransition metal ionic compound into the space containing the exhaustedgas, while agitating air if necessary, and then conducting lightirradiation in the presence of water vapor. In this case, insolublematter can be removed using a dust collector, etc., if necessary.Alternatively, it is possible to purify the exhausted gas by bubbling itthrough a solution containing Compound (i) and a transition metal ioniccompound, and then conducting light irradiation. Insoluble matter isseparated/collected, if necessary.

Alternatively, it is possible to contact organic chemical-containingcontaminated substance with Compound (i) or (ii) by, for example,passing an exhausted gas through carriers supporting either or bothCompounds (i) and (ii).

When the contaminant is a water-insoluble liquid such as oil, etc., theorganic chemical-containing oil can be purified by emulsifying them withan aqueous solution containing Compound (i) and a transition metal ioniccompound by using a known emulsifier, emulsification equipment, etc.,conducting light irradiation, and then separating/collecting insolublematter if necessary.

An object of applying the technique of the present invention toagricultural products and like foodstuffs is to remove or detoxifyagricultural chemicals remaining on leaves of vegetables, fruits, etc.For example, in the case of vegetables grown in fields, a mixture ofCompound (i) and a transition metal ionic compound is sprayed onto thevegetables. This makes it possible to decompose the organic chemicals toform insoluble particles when exposed to sunlight. In this case,insoluble matter from the organic chemicals can be removed by washingthe vegetables.

By employing the technique of the present invention, the waste generatedin a space station or like space facility can be handled in space,particularly by using sun light containing ultra violet light. In manycases, conditions suitable for growing microorganisms cannot bemaintained in space, and therefore it is difficult to treat organicchemicals by known biological methods. In contrast, the method of thepresent invention can effectively decompose organic chemicals by verysimple steps without using microorganisms.

The temperature for treating organic chemicals in the present inventionis not limited, and it may be an ambient temperature (room temperature).

2. System for Purifying Organic Chemical-Containing ContaminatedSubstance

The present invention also provides a system (apparatus) for purifyingorganic chemicals used in the above-mentioned method for decomposingorganic chemicals.

The system of the present invention comprises a photoreaction reactorand, if necessary, an insoluble matter separation/collection apparatus.The photoreaction reactor is provided with a supply port(s) and anoutlet(s), whereby the contaminated substance containing organicchemicals, Compound (i), and a transition metal ionic compound aresupplied into the photoreaction reactor through the supply port(s), andthey are exhausted from the outlet(s) after being treated. The supplyport(s) and the outlet(s) may be provided separately or one opening mayserve both functions.

There is no limitation on the form of the photoreaction reactor and itmay be a bath, tank, etc. It is also possible to use a tube (pipe) asthe photoreaction reactor that can mix a contaminated substancecontaining organic chemicals, Compound (i), a transition metal ioniccompound, and water, if necessary, and flow the mixture from the supplyport(s) to the outlet(s). Lakes or lagoons may also be used.

The photoreaction reactor is provided with a mixer for obtaining amixture of organic chemicals and Compound (i) and a transition metalionic compound, and a light irradiator for irradiating the mixture withlight. There is no limitation to the mixer and a conventionally knownmixing means, such as a stirrer, can be employed. There is no limitationto the light irradiator as long as it can conduct light irradiationunder the conditions as described above. Examples of usable lightirradiators include fluorescent lights, germicidal lamps, mercury lamps,deuterium lamps, xenon lamps, halogen lamps, tungsten lamps, LEDs, etc.,but are not limited those. Natural light such as sun light may also beused as light irradiators. As described above, (ii) a transition metalionic compound may be supplied to a photoreaction reactor together withCompound (i) and an organic chemical-containing contaminated substance,or supplied to the mixture of Compound (i) and an organicchemical-containing contaminated substance after irradiation of light.In the photoreaction reactor, organic chemicals are detoxified by beingirradiated with light, and insolubilized by the transition metal ioniccompound, forming solid matter.

The system of the present invention may comprise an apparatus forseparating/collecting insoluble matter, if necessary, toseparate/collect insoluble matter generated in the photoreactionreactor. The separation/collection apparatus is connected to thephotoreaction reactor in such a manner that the mixture irradiated withlight in the photoreaction reactor is transferred from the outlet of thephotoreaction reactor to the separation/collection apparatus. Insolublematter generated in the mixture in the photoreaction reactor isseparated/collected by the separation/collection apparatus. Thethus-obtained processed substance does not contain organic chemicals andis therefore purified.

Examples of usable separation/collection apparatuses include dustcollectors, filtration apparatuses, columns, cyclone separators,centrifugal separators, etc., but are not limited to those. Theconstruction of the system of the present invention is shown in FIG. 1.

EXAMPLES

The present invention is explained in detail by showing Examples.However, the present invention is not limited to Examples below.

Example 1 Decomposition and Separation/Collection of 2,4-Dichlorophenol

2,4-dichlorophenol was added to 20 ml of purified water placed in a 100ml beaker in such a manner that the concentration of the2,4-dichlorophenol became 1 mM. Subsequently, calcium hydroxide andcobalt chloride were added to the mixture in such a manner that theconcentration of calcium hydroxide became 2 mM and that of cobaltchloride became 1 mM followed by stirring sufficiently. A 15 Wgermicidal lamp (GL-15, product of Matsushita Electric Industrial Co.,Ltd.) was placed 14 cm away from the water surface of the beaker, andthe aqueous solution containing 2,4-dichlorophenol was irradiated withultraviolet light while stirring using a stirrer. Samples were collectedbefore and after irradiation of ultraviolet light. The samples subjectedto 60 minutes irradiation became brown suspensions. These suspensionswere subjected to filtration using two types of filter papers No. 2 andNo. 5C (product of Advantec), and the optical densities of thethus-obtained filtrates at 400 nm were measured using an absorptiometerU-2000 (product of Hitachi). The concentration of 2,4-dichorolophenol inthe filtrate was measured by using a high-performance liquidchromatography (product of Hitachi).

As a result, 90% or more of 2,4-dichrolophenol was reduced. As shown inFIG. 2, solid matter (insoluble matter from the decomposed organicchemicals) were separated/collected on the filter papers by addingcobalt chloride. Optical densities of the filtrates were measured,revealing that those filtrates to which cobalt chloride was not addedhad an optical density almost the same as that of the suspension, butthat filtrate to which cobalt chloride (CoCl₂) was added had opticaldensities about ¼^(th) that of the suspension respectively (see FIG. 3).From the fact that the filter papers No. 2 and No. 5C have particleholding sizes (minimum particle diameter of the particles retained bythe filter paper and which do not flow into the filtrate) were about 5μm and about 1 μm respectively, it became clear that solid matter largerthan 5 μm is formed by adding cobalt chloride and such solid matter canbe removed by filtration.

Instead of using a filter paper, the brown suspensions could be passedthrough a glass column (diameter: 5 cm, length: 10 cm) filled with 30-50mesh sea sand (product of Nacalai Tesque, Inc.) to the height of 5 cm.As a result, solid matter in the suspensions was completelyseparated/collected, giving transparent filtrates.

Example 2 Decomposition of Various Organic Chemicals

Bisphenol A was added to 50 ml of purified water placed in a 100 mlbeaker in such a manner that the concentration of the bisphenol A became100 μM. Subsequently, 0.20 g of dolomite was added to the mixture andstirred. A 15 W germicidal lamp (GL-15, product of Matsushita ElectricIndustrial Co., Ltd.) was placed cm away from the water surface of thebeaker, and the resultant aqueous solution was irradiated withultraviolet light while stirring using a stirrer. Samples were collectedbefore and after irradiation of ultraviolet light.

(a) Measurement of a Decomposition Rate

The collected samples were subjected to centrifugal separation (10000rmp, 5 minutes) to collect the supernatants. To 135 μl of supernatantwas added 15 μl of HCl (6 N). The concentration of bisphenol A wasmeasured using high performance liquid chromatography (HPLC). The extentof decomposition was determined from measurement at 280 nm using areversed phase column (5C18-AR-II, product of Nacalai Tesque, Inc.)through which methanol/water=50/50 (v/v) was eluted as the mobile phaseat 1 ml/min, and 10 μl of each sample was injected.

(b) Decomposition of Various Organic Chemicals

In the same manner, the extents of decomposition of tetrachlorobisphenolA; o-chlorophenol; p-chlorophenol; 2,4-dichlorophenol;p-tert-butylphenol; 2, 4-dichlorophenoxy acetic acid (2,4-D);carbendazim; 17-β-estradiol; 1-naphthol and 3,5-xylenol were determined(irradiation with UV, dolomite added). For comparison, the extents ofdecomposition of the same organic chemicals were determined withoutadding dolomite (only irradiation of ultraviolet light). The extent ofdecomposition is expressed as the percentage reduction after 60 minutesof reaction from the initial concentration of each organic chemical.

Table 1 shows the results. As shown in Table 1, various endocrinedisruptor compounds were decomposed satisfactory. Furthermore, from thefact that decomposition of 2,4-dichlorophenol and tetrachlorobisphenol Aboth having a plurality of chlorine substituents were also accelerated,it can be concluded that decomposition of various other photodegradablechlorinated compounds with a plurality of chlorine substituents, such asdioxins and PCBs, can also be accelerated.

TABLE 1 Initital concentration 60 minutes of decomposition OrganicChemicals (μM) UV + Dolomite UV only Bisphenol A 100 70 0Tetrachrolobisphenol A 50 100 31 o-Chlorophenol 100 100 28p-Chlorophenol 100 100 52 2,4-Dichlorophenol 100 100 0p-tert-Butylphenol 100 94 18 2,4-D 100 13 6 Carbendazim 40 88 817-β-Estradiol 10 100 0 1-Naphthol 100 94 32 3,5-Xylenol 100 51 7

Example 3 Decomposition Using Various Compound (i)

To 50 ml of pure water placed in a 100 ml beaker was added bisphenol A(BPA) to a concentration of 100 μM. Subsequently, 44 mg of calciumoxide, 58 mg of calcium hydroxide, 25 mg of magnesium oxide, 36 mg ofmagnesium hydroxide, 52 mg of magnesium carbonate or 63 mg of sodiumhydroxide was added to a beaker. A 15 W germicidal lamp (GL-15, productof Matsushita Electric Industrial Co., Ltd.) was placed 12 cm away fromthe water surface of the beaker, and the resultant aqueous solution wasirradiated with ultraviolet light while stirring using a stirrer.Samples were collected every 20 minutes.

As a result, as shown in FIG. 4, it became clear that bisphenol A can bedecomposed by using alkali metal compounds and/or alkaline-earth metalcompounds.

Example 4 Decomposition and Separation/Collection Using Various Compound(i)

Cobalt chloride was added to 20 ml of 1 mM 2,4-dichlorophenol in thesame manner as in Example 1 in such a manner that the concentration ofthe cobalt chloride became 1 mM. Instead of calcium hydroxide, onemember selected from calcium oxide, calcium carbonate, magnesiumhydroxide, magnesium oxide, magnesium carbonate, potassium hydroxide,and sodium hydroxide was added to the resultant mixture in such a mannerthat its concentration became 2 mM. Alternatively, 4 mg of dolomite maybe added to the mixture. The mixtures were irradiated with ultravioletlight for 60 minutes, and then subjected to filtration using two typesof filter papers No. 2 and No. 5C. Optical densities of thethus-obtained filtrates at 400 nm were measured.

As a result, all samples to which a metallic compound of calcium,magnesium, potassium or sodium, or dolomite was added became brownsuspensions. Optical densities of the filtrates obtained by subjectingthe resultant suspensions to filtration were measured, revealing that,as shown in FIG. 5, formation of solid matter was also facilitated whenone of these metallic compounds or dolomite was added as when a calciumhydroxide (Ca(OH)2) was added. Therefore, it is believed that metalliccompounds of calcium, magnesium, potassium, and sodium, and variousminerals containing such metallic compound(s) can achieve such effects.

Example 5 Decomposition and Separation/Collection Using VariousTransition Metals

Calcium hydroxide was added to 1 mM 2,4-dichlorophenol in the samemanner as in Example 1 in such a manner that the concentration of thecalcium hydroxide became 2 mM. Instead of cobalt chloride, one memberselected from cobalt nitrate, manganese chloride, manganese nitrate,ferric chloride, iron ferric nitrate, nickel chloride, nickel nitrate,copper chloride, copper nitrate, zinc chloride, zinc nitrate, titaniumoxide, and ferric oxide was added to the resultant mixture so that itsconcentration became 1 mM. The resultant mixtures were subjected to 60minutes irradiation and the resultant suspensions were then filteredusing two types of filter papers No. 2 and No. 5C. The optical densitiesof the thus-obtained filtrates at 400 nm were measured using.

As a result, all samples to which a chloride salt or a nitrate salt oftransition metal was added became brown suspensions. Optical densitiesof the filtrates obtained by subjecting the resultant suspensions tofiltration were measured. As shown in FIG. 6, in all samples to which achloride salt or a nitrate salt of transition metal was added, theoptical densities of the filtrates obtained by using filter papers No. 2and No. 5C were significantly reduced compared to that of thesuspension. However, when the same experiments were conducted using atitanium oxide and an ferric oxide, which are often used asphotocatalysts and/or oxidation catalysts, any facilitatory effects forforming solid matter were not observed. Titanium oxides and ferricoxides do not achieve such effect presumably because they axe insolublein water. The effects of addition of a chloride salt or a nitrate saltare described in this example; however, it can be easily concluded thatformation of solid matter can be facilitated by adding any transitionmetal compounds that form ions when dissolved in water.

Example 6 Decomposition and Separation/Collection of Various OrganicChemicals

In the same manner as in Example 1, bisphenol A instead of2,4-dichlorophenol was added so as to have a concentration of 0.5 mM.Subsequently, calcium hydroxide and cobalt chloride were added to have aconcentration of 2 mm and 1 mM respectively. After conducting 60 minutesultraviolet light irradiation, the resultant suspensions were subjectedto filtration using two types of filter papers No. 2 and No. 5C, and theoptical densities of the thus obtained filtrates at 400 nm weremeasured.

In the same manner, each of o-chlorophenol; p-chlorophenol; p-tert-butylphenol; 1-naphthol; 3,5-xylenol; and 2, 4-dichlorophenoxy acetic acid(2,4-D) were added so as to have a concentration of 1 mM. Afterirradiation of ultraviolet light, the optical densities of the resultantsuspensions were measured.

FIG. 7 shows the results. These organic chemicals were satisfactorydecomposed and solid matter was formed. Therefore, it became clear thatthis method is applicable to decompose organic chemicals. Furthermore,because all these organic chemicals are endocrine disruptors, it can beconcluded that this method is also effective for decomposing aromaticcompounds comprising other endocrine disruptors having a similarconstruction. Furthermore, considering the fact that decomposition ofchlorophenols having at least one chloro-substituent, decomposition of2,4-D, and formation of solid matter can be facilitated, this method isalso applicable to treat various photodegradable organic chemicalshaving chloro-substituent.

Example 7 Treatment of Solid Contaminated-Substance Containing OrganicChemicals

An example of evaluation of treatment of solid contaminated-substancecontaining organic chemicals, such as contaminated soil, sludge, andincinerated ash, was explained below. To 20 g of sea sand (30-50 mesh,product of Nacalai Tesque, Inc.) was added 10 ml of 1 mM2,4-dichlorophenol solution, followed by sufficient stirring. Water (10ml) containing 4 mM calcium hydroxide and 2 mM cobalt chloride was addedto the resultant mixture to give slurry, and the obtained slurry wasplaced in a cylindrical quartz tube. The slurry was irradiated withultraviolet light for 60 minutes using a germicidal lamp placed 10 cmaway therefrom while agitating by rotation. After the reaction, theslurry was subjected to 2,4-dichlorophenol extraction using methanol,and the 2,4-dichlorophenol concentration was then measured using ahigh-performance liquid chromatography.

After 60 minutes irradiation of ultraviolet light, the concentration of2,4-dichlorophenol was reduced to 1/10^(th). Photographs before andafter irradiation of ultraviolet light are shown in FIG. 8. The sea sandwas white before ultraviolet light irradiation but it became brown afterthe irradiation. This indicates that insoluble solid matter was formedfrom 2,4-dichlorophenol. This result made it clear that solidcontaminated-substance containing organic chemicals can be purified byirradiating it with ultraviolet light after forming it into slurry.

Example 8 Verification of Polymerization

In order to verify the occurrence of polymerization, a solutionirradiated with ultraviolet light after adding calcium hydroxide andcobalt chloride to bisphenol A was inspected using a high-performanceliquid chromatograph mass spectrometer (NanoFrontier LD, product ofHitachi).

FIG. 9 shows the results. Peaks at mass numbers of 453 and 679, whichare presumably attributable to a dimer and a trimer of bisphenol A, areobserved. This confirms the occurrence of polymerization of bisphenol A.The structural formulae shown at the right of the figure are examples ofthe expected dimer and trimer. Peaks attributable to higher thantetramer were not observed. Presumably, this is because such substanceshave high molecular weights and are insoluble in solvent. From theseresults, it can be concluded that insoluble matter is formed in thisreaction due to polymerization of organic chemicals.

Example 9 Timing for Adding Transition Metal Compound

Calcium hydroxide was added to 20 ml of 1 mM 2,4-dichlorophenol in thesame manner as in Example 1 to have a concentration of 2 mM. Cobaltchloride was added to the resultant mixture to have a concentration of 1mM, and then the solution was irradiated with ultraviolet light whilestirring for 60 minutes. After irradiation of ultraviolet light, thesolution was stirred for 60 minutes (this sample is referred to asBefore UV). Alternatively, the mixture of calcium hydroxide and2,4-dichlorophenol was irradiated with ultraviolet light for 60 minutesand cobalt chloride was then added thereto so that the concentrationthereof became 1 mM, and then was stirred for 60 minutes (this sample isreferred to as After UV). Another sample was obtained by irradiatingultraviolet light for 60 minutes without adding cobalt chloride, andthen the resultant suspension was stirred for 60 minutes (this sample isreferred to as Nothing). These samples were subjected to filtrationusing two types of filter papers No. 2 and No. 5C, and the opticaldensities of the thus obtained filtrates at 400 nm were measured.

The result reveals that even a case when cobalt chloride was added afterirradiation of ultraviolet light (After UV), formation of insolublematter was also facilitated (FIG. 10). Therefore, it can be concludedthat the preferable timing for adding a transition metal compound isbefore irradiation of ultraviolet light but it is still effective evenafter irradiation of ultraviolet light.

Example 10 Treatment of Dioxin and PCB

In the same manner as in Example 1, to 50 ml of purified water placed ina 100 ml beaker, a PCB mixture (KC-400, product of Kaneka Corporation)was added so as to have a concentration of 0.02 mg/L, or2,3-dichlorodibenzo-p-dioxin (product of Supelco, Inc.) was added so asto have a concentration of 0.01 mg/L instead of 2,4-dichlorophenol.Subsequently, calcium hydroxide and cobalt chloride were added to have aconcentration of 2 mM and 1 mM respectively. A 15 W germicidal lamp wasplaced 12 cm away from the water surface of the glass beaker, and theresultant aqueous solution was irradiated with ultraviolet light whilestirring using a stirrer for 20 minutes. After ultraviolet lightirradiation, samples were collected and concentrated by solid phaseextraction. Concentrations of dioxin and PCB were measured with a gaschromatograph mass spectrometer (GC-MS).

With regard to the samples subjected to only ultraviolet lightirradiation, the extent of removal of PCBs having 1 to 5 chlorines was34-64%, and that of 2,3-dichlorodibenzo-p-dioxin was about 87%. Incontrast, by irradiating the samples with ultraviolet light after addingcalcium hydroxide and cobalt chloride, the extents of removal of thePCBs and dioxin were increased to 98-100%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a treatment system of the present invention.

FIG. 2 is a photograph of filtered insoluble matter generated bydecomposition of 2,4-dichlorophenol.

FIG. 3 is a graph showing that insolubilization of decomposed organicchemical is accelerated by addition of cobalt chloride.

FIG. 4 is a graph showing that bisphenol A can be decomposed by additionof various metal compounds (i).

FIG. 5 is a graph showing that insolubilization of 2,4-dichlorophenol isaccelerated by addition of various metal compounds (1).

FIG. 6 is a graph showing that insolubilization of 2,4-dichlorophenol isaccelerated by addition of various transition metal salts.

FIG. 7 is a graph showing that insolubilization of various organicchemicals can be accelerated.

FIG. 8 is a picture showing that a solid contaminated substancecontaining organic chemicals can be treated.

FIG. 9 shows formation of polymerization products of bisphenol A.

FIG. 10 is a graph showing formation of insoluble matter when a cobaltsalt is added after irradiation of ultraviolet light (After UV).

1-18. (canceled)
 19. A method for purifying an aromaticcompound-containing contaminated substance comprising: a first step ofirradiating the aromatic compound-containing contaminated substance withlight in the presence of (i) at least one water-soluble alkali metalcompound and/or at least one water-soluble alkaline-earth metal compoundselected from the group consisting of calcium compounds, magnesiumcompounds, potassium compounds, and sodium compounds, and (ii) ironcompound, whereby the aromatic compound is polymerized, wherein ironbecomes ions in an aqueous solution, and a second step of collecting thepolymerized aromatic compound that is generated in the first step. 20.The method according to claim 1, wherein the first step comprises thesteps of: (1) a step of adding the compound (i), and the compound (ii);and (2) a step of irradiating a mixture obtained in the first step withlight.
 21. The method according to claim 1, wherein the method furthercomprises a step of separating the polymerized aromatic compound betweenthe first step and the second step.
 22. The method according to claim 1,wherein at least one of the compounds (i) and (ii) is adhered to acarrier.
 23. The method according to claim 1, wherein a compoundcomprising the compound (ii) adhered to the compound (i) is used ascompounds (i) and (ii).
 24. The method according to claim 1, wherein thecompound (i) is dolomite.
 25. The method according to claim 1, whereinthe compound (i) is at least one member selected from the groupconsisting of dolomite, water-soluble compounds of hydroxides,inorganic-acid salts, organic acid salts and oxides of calcium,magnesium, potassium, and sodium.
 26. The method according to claim 1,wherein the transition metal ionic compound is at least one compoundselected from the group consisting of ferric chloride, iron nitrate,iron hydroxide, iron phosphate, iron ethylenediaminetetraacetate, andiron sulfate.
 27. The method according to claim 1, wherein the aromaticcompound is at least one member selected from the group consisting of apolychlorinated biphenyl (PCB), dioxin, o-chlorophenol, p-chlorophenol,2,4-dichlorophenol, p-tert-butylphenol, 1-naphthol, 3,5-xylenol,carbendazim, 17[beta]-estradiol, and bisphenol A.
 28. The methodaccording to claim 1, wherein the light used for light irradiation isultraviolet.
 29. The method according to claim 1, wherein the aromaticcompound-containing contaminated substance is at least one memberselected from the group consisting of factory effluents, agriculturaleffluents, domestic drainage, sewage, leachate from waste disposalsites, exhaust gases, contaminated soil, sludge, and incinerated ash.30. A method for purifying an aromatic compound-containing contaminatedsubstance wherein the method comprises the steps of: (I) irradiating thearomatic compound-containing contaminated substance with light in thepresence of (i) at least one water-soluble alkali metal compound and/orat least one water-soluble alkaline-earth metal compound selected fromthe group consisting of calcium compounds, magnesium compounds,potassium compounds, and sodium compounds; and then (II) adding (ii)iron compounds, whereby the aromatic compound is polymerized, whereiniron becomes ions in an aqueous solution, and (III) collecting thepolymerized aromatic compound that is generated in step (II).
 31. Themethod according to claim 12, wherein the method further comprises (IV)separating the polymerized aromatic compound contained in contaminatedsubstance between (II) and (III).
 32. The method according to claim 12,wherein at least one of the compounds (i) and (ii) is adhered to acarrier.
 33. The method according to claim 12, wherein the compound (i)is dolomite.
 34. The method according to claim 12, wherein the compound(i) is at least one member selected from the group consisting ofdolomite, water-soluble compounds of hydroxides, inorganic-acid salts,organic acid salts and oxides of calcium, magnesium, potassium, andsodium.
 35. The method according to claim 12, wherein the transitionmetal ionic compound is at least one compound selected from the groupconsisting of ferric chloride, iron nitrate, iron hydroxide, ironphosphate, iron ethylenediaminetetraacetate, and iron sulfate.
 36. Themethod according to claim 12, wherein the aromatic compound is at leastone member selected from the group consisting of a polychlorinatedbiphenyl (PCB), dioxin, o-chlorophenol, p-chlorophenol,2,4-dichlorophenol, p-tert-butylphenol, 1-naphthol, 3,5-xylenol,carbendazim, 17[beta]-estradiol, and bisphenol A.
 37. The methodaccording to claim 12, wherein the light used for light irradiation isultraviolet.